Macromolecules, Vol.34, No.20, 7172-7178, 2001
Noncovalently connected polymeric micelles based on a homopolymer pair in solutions
The intermolecular complexes with poly(4-vinylpyridine) (PVPy) as the backbone and carboxyl-terminated polybutadiene (CPB) as the grafts were formed due to hydrogen bonding in their common solvent chloroform. Two solvent pairs, i.e., n-hexane/chloroform and nitromethane/chloroform, were found selective for CPB and PVPy, respectively. Thus, the stable micelles with PVPy being the core and CPB being the shell, denoted as (PVPy)-CPB, and the ones with CPB core and PVPy shell, denoted as (CPB)-PVPy, were formed in the corresponding selective solvent pairs. Differing from the conventional micelles made of block or graft copolymers, the present micelles possess hydrogen bonds instead of covalent bonds connecting the core and shell and their composition; i.e., the weight ratio of the core to shell is readily adjustable. Dynamic light scattering study demonstrated that the average hydrodynamic diameters
of the micelles were mostly in the range from 100 to 300 nm depending on the solvent composition, polymer concentration, and the chain number ratio of CPB to PVPy, etc. (PVPy)-CPB were found more stable against dilution than (CPB)-PVPy. The two kinds of micelles differ in their diameter-composition dependence; namely, with increasing the ratio of CPB/PVPy, of (PVPy)-CPB decreases monotonically while that of (CPB)-PVPy increases at the low ratio range but decreases at the high ratio range. Besides, the core-shell structure of both micelles was clearly visualized by transmission electronic microscopy using staining techniques.